Long-term variation of temperature over North China and its links with large-scale atmospheric circulation

A May-July temperature reconstruction is based on tree-ring widths of Chinese pine (Pinus tabulaeformis) from Ningwu, Shanxi Province, China. The reconstruction explains 45.1% of the variance in observed May-July temperature. The intervals with persistent decadal warmth include 1779-1792, 1827-1839, 1853-1865, 1898-1932, 1936-1948 and 1987-2003. Intervals with persistent decadal cold include 1793-1807, 1814-1826, 1866-1888, 1949-1963 and 1976-1986. Spatial correlation between the reconstruction and the gridded temperature datasets reveals that the reconstruction is representative of temperature variability in semi-arid/arid regions of East Asia, including the Gobi Desert, the Loess Plateau and the North China Plain. The regions are referred to as North China in this study. Significant correlation with the January-August temperature reconstruction in the Helan Mountains of Northwest China for the overlapping period of 1796-1999 suggests that the reconstruction captures the regional temperature variability for a long-term period. The reconstructed temperature series has a significantly negative correlation with the monsoon rainfall series at inter-annual, decadal and multi-decadal time scales for the overlapping period of 1688-2003, suggesting an influence of the East Asian Summer Monsoon (EASM) and the dominant climate regime consisting of either cool/wet or warm/dry weather in the North China. Moreover, for the past three centuries, synchronous variations are found for the reconstructed temperature as well as the reconstructed Asian-Pacific Oscillation (APO) and the Pacific Decadal Oscillation (PDO) at decadal and multi-decadal time scales, suggesting the influences of large-scale atmospheric circulations on temperature variability in the North China. The possible mechanisms behind these links are also explained with observed climate data.</p

Tree-ring derived temperature records in the central Loess Plateau, China

Using tree-ring widths of Pinus tabulaeformis Carr. trees, mean temperatures from February to September were reconstructed for the Kongtong Mountain during the past 283 years. The reconstruction could explain 43.7% of temperature variance during the calibration period from 1951 to 2004. It displays similar patterns to several temperature reconstructions in the Loess Plateau. It corresponds well with the temperature regimes in Hokkaido, Japan, indicating that both regions have similar warm and cold intervals. The high correlation between the reconstruction and the CRU (Climatic Research Unit of University of East Anglia, UK) TS3 temperature datasets showed that the temperature reconstruction could be representative of large-scale climate change over northern China. In addition, the Pacific Decadal Oscillation (PDO) affected temperature variations of northern China and even Hokkaido to a certain extent.</p

Annual precipitation in Liancheng, China, since 1777 AD derived from tree rings of Chinese pine (Pinus tabulaeformis Carr.)

Precipitation from the previous August to the current June over the last 232 years in Liancheng, China, was reconstructed by a transfer function based on the correlation between tree-ring widths and local meteorological data. The explained variance was 45.3 %, and fluctuations on both annual and decadal scales were captured. Wet periods with precipitation above the 232-year mean occurred from 1777 to 1785, 1802 to 1818, 1844 to 1861, 1889 to 1922 and 1939 to 1960. Dry periods (precipitation below the mean) occurred from 1786 to 1801, 1819 to 1843, 1862 to 1888 and 1923 to 1938. The reconstruction compares well with a tree-ring-based precipitation reconstruction at Mt. Xinglong; both of them showed the well-known severe drought in the late 1920s. The rainfall series also shows highly synchronous decreasing trends since the 1940s, suggesting that precipitation related to the East Asian summer monsoon at these two sites has decreased by large spatial and temporal (decadal) scales. Power spectrum analysis of the reconstruction showed remarkable 21.82-, 3.48-, 3.12-, 3.08- and 2.31-year cycles for the past 232 years; the 22-year cycle corresponds to the solar cycle and is expressed widely in tree ring/precipitation reconstructions on the China Loess Plateau. This may suggest a solar influence on the precipitation variations on the Loess Plateau, although the mechanisms are not well understood.</p

Regional hydroclimate and precipitation delta O-18 revealed in tree-ring cellulose delta O-18 from different tree species in semi-arid Northern China

Oxygen isotopic ratios (delta(18)O) of tree-ring cellulose, grown from 1954 to 2003 in semi-arid Northern China demonstrate a common inter-annual variability, despite coming from three different species in two distinct growth environments (an alpine meadow and a rocky ridge). The variability was significantly negative correlated with precipitation and relative humidity during the growing season. This suggests that the past summer hydroclimate can be inferred from tree-ring cellulose delta(18)O from various kinds of trees growing in semi-arid Northern China. In addition, we evaluated past changes in delta(18)O of precipitation from the tree-ring cellulose delta(18)O and relative humidity using the mechanistic model for tree-ring cellulose delta(18)O in Roden et al. (2000). By fixing the species-dependent exchange rate of oxygen between carbohydrate and xylem water for Larix principis-rupprechtii and Picea koraiensis, we could also reconstruct the variations in precipitation delta(18)O from the different tree species, which are similar to the observed delta(18)O of precipitation during 1985-2002. Although the reconstructed delta(18)O of precipitation does not have any significant relation to local temperature or precipitation during 1954-2003, its long-term variation pattern is similar to that of the Asian summer monsoon indices and delta(18)O of stalagmite in the Heshang cave (30 degrees 27&#39;N, 110 degrees 25&#39;E; Fig. 1), suggesting that delta(18)O of precipitation is not controlled by local meteorology but is influenced by large-scale atmospheric circulation.</p

Amplitudes, rates, periodicities and causes of temperature variations in the past 2485 years and future trends over the central-eastern Tibetan Plateau

Amplitudes, rates, periodicities, causes and future trends of temperature variations based on tree rings for the past 2485 years on the central-eastern Tibetan Plateau were analyzed. The results showed that extreme climatic events on the Plateau, such as the Medieval Warm Period, Little Ice Age and 20th Century Warming appeared synchronously with those in other places worldwide. The largest amplitude and rate of temperature change occurred during the Eastern Jin Event (343-425 AD), and not in the late 20th century. There were significant cycles of 1324 a, 800 a, 199 a, 110 a and 2-3 a in the 2485-year temperature series. The 1324 a, 800 a, 199 a and 110 a cycles are associated with solar activity, which greatly affects the Earth surface temperature. The long-term trends (&gt;1000 a) of temperature were controlled by the millennium-scale cycle, and amplitudes were dominated by multi-century cycles. Moreover, cold intervals corresponded to sunspot minimums. The prediction indicated that the temperature will decrease in the future until to 2068 AD and then increase again.</p

Hydroclimate variability in the North China Plain and its link with El Nino-Southern Oscillation since 1784 AD: Insights from tree-ring cellulose delta(18)O

We present here a chronology of tree-ring cellulose delta(18)O from 1784 to 2003 that is based on the individual measurements of five Larix principis-rupprechtii trees growing in the semiarid North China Plain (NCP; 34 degrees-41 degrees N, 107 degrees-120 degrees E). This chronology has a significant, negative correlation with summer precipitation, relative humidity, and the Palmer Drought Severity Index. It is representative of regional summer hydroclimate variability in the NCP by analyzing its spatial correlation patterns with CRU TS3 precipitation grid data sets. Historically, extreme climate events (drought and flood) could be detected by the high-frequency (annual) signals in the chronology. The low-frequency (11 year moving average) signals are consistent with the time series of the drought frequency and the regional dryness-wetness index derived from historical documents in the NCP. Significant spatial correlation patterns of measured precipitation and the tree-ring cellulose delta(18)O chronology from the NCP with observed sea surface temperature in the eastern equatorial Pacific during the 1954-2003 and 1854-2003 periods suggest that the summer hydroclimate of the NCP has a close link with El Nino-Southern Oscillation. Mostly extreme dry or wet years identified by the chronology follow historical El Nino or La Nina events over the past 220 years, respectively.</p

Tree-Ring Based May-July Temperature Reconstruction Since AD 1630 on the Western Loess Plateau, China

Tree-ring samples from Chinese Pine (Pinus tabulaeformis Carr.) collected at Mt. Shimen on the western Loess Plateau, China, were used to reconstruct the mean May-July temperature during AD 1630-2011. The regression model explained 48% of the adjusted variance in the instrumentally observed mean May-July temperature. The reconstruction revealed significant temperature variations at interannual to decadal scales. Cool periods observed in the reconstruction coincided with reduced solar activities. The reconstructed temperature matched well with two other tree-ring based temperature reconstructions conducted on the northern slope of the Qinling Mountains (on the southern margin of the Loess Plateau of China) for both annual and decadal scales. In addition, this study agreed well with several series derived from different proxies. This reconstruction improves upon the sparse network of high-resolution paleoclimatic records for the western Loess Plateau, China.</p

Individual and pooled tree-ring stable-carbon isotope series in Chinese pine from the Nan Wutai region, China: Common signal and climate relationships

To investigate the differences in the climatic signals in stable-carbon isotopic composition captured by averaging series from individual trees versus raw wood of trees pooled prior to analysis, we analyzed two groups of Chinese pine (Pinus tabulaeformis Carr.) from the Nan Wutai region of the Qinling Mountains, China. One group included three trees that were analyzed separately, and the other group comprised four other trees that were pooled prior to preparation and analysis. All &delta;13C series were positively correlated (r = 0.50&ndash;0.58, p &lt; 0.0001) for the period AD 1901&ndash;2003. After removing the effects of changing &delta;13C of atmospheric CO2, correlations between the meteorological data and all individual and pooled discrimination (∆13C) series revealed significant negative responses to temperature for several specific months and for mean January to September (TJ&ndash;S) temperature. We used a &ldquo;numerical mix method&rdquo; (NMM, equivalent to unweighted mean), by averaging individual ∆13C series (NPS1+NPS2+NPS3), to generate a new series that more strongly correlated to climate series TJ&ndash;S (r = &minus; 0.67, p &lt; 0.0001). This time interval from January through September (J&ndash;S) includes the growing season and months prior to the growing season, but the temperature prior to the growing season may provide energy necessary for timely initiation of growth. Thus, the mean TJ&ndash;S is significant for plant growth and is consistent with the tree physiology in this region. Our results suggest that the numerical mix method with tree-ring stable isotope data from three trees provides a series quite satisfactory for climatic reconstruction. The relationship of the numerical mix model ∆13C with temperature was stronger than for the pooled series, suggesting numerical mixing of series can be more effective than raw wood sample pooling at least according to the trees in this study.</p

Tree-ring stable carbon isotope-based May-July temperature reconstruction over Nanwutai, China, for the past century and its record of 20th century warming

Growth anomaly of trees in some regions was detected under current episode of rapid warming. This raises a dilemma for temperature reconstructions by using tree-ring width which is believed to be the most important proxy on inter-annual temperature reconstruction during the past millenniums. Here we employed the tree-ring &delta;13C to reconstruct temperature variations for exploring their potential on capturing signals of rapid warming, and to test how its difference with the tree-ring width based reconstruction. In this study the mean May-July temperature (TM-J) was reconstructed over the past century by tree-ring &delta;13C of Chinese pine trees growing in the Nanwutai region. The explained variance of the reconstruction was 43.3% (42.1% after adjusting the degrees of freedom). Compared to a ring-width temperature reconstruction (May-July) from the same site, the tree-ring &delta;13C-based temperature reconstruction offered two distinct advantages: 1) it captured a wider range of temperature variability, i.e., at least May-July, even over a longer part of the year, January-September; and 2) the reconstruction preserved more low-frequency climate information than that of ring width did.The 20th century warming was well represented in the Nanwutai tree-ring &delta;13C temperature reconstruction, which implied that stable carbon isotope of tree rings potentially represents temperature variations during historical episodes of rapid warming. A spatial correlation analysis showed that our temperature reconstruction represented climate variations over the entire Loess Plateau in north-central China. Significant positive correlations (p&lt;0.1) were found between the temperature reconstruction and ENSO, as well as SSTs in the Pacific and Indian Oceans. The reconstruction showed the periodicities of 22.78-, 4.16-, 3.45-3.97- and 2.04-2.83-year quasi-cycles at a 95% confidence level. Our results suggested that temperature variability in the Nanwutai region may be linked to Pacific and Indian Ocean SST variations and solar activity.</p